Photovoltaic arrays require internal by-pass diodes to increase reliability. The diodes serve to make possible desirable reverse current flows which allow the series string to function in the case of a cell open circuit. A typical circuit employs a by-pass loop with a single diode around each solar cell or a series of cells. Note that if a cell is damaged so that the cell becomes an open circuit, the by-pass diode permits current flow in the series string. Thus, with by-pass diodes in the circuit, a failure of a single cell does not cause the failure of all the cells in the string. For the case of the shading of the cell, the by-pass diode prevents a cell string from overheating owing to the reverse bias condition that results from the shadow. Survivable space arrays of solar cells require by-pass diodes in order to prevent string failure owing to the failure of a single cell during high temperature events or other threats to efficient device operation.
It is known that solar cell by-pass diodes have used discrete components where the diode for each solar cell is placed in proximity to another cell in the array to prevent the failure of both the solar cell and its by-pass diode.
Desirable features of by-pass diodes are the following: highest possible forward bias saturation current, and lowest possible reverse saturation current. Low reverse saturation current reduces the parasitic losses from the by-pass diode during ordinary operation (in which the by-pass diode is in reverse bias), while high forward current yields low losses in the by-pass diode when it is in forward bias and compensating for a failed cell. Other desirable features of by-pass diodes include high current carrying ability, fast turn-on time, and small size. Existing by-pass diodes are generally discrete components that fail to maintain device performance at high temperatures. Thus there is a need for a diode structure that can operate or survive a high temperature environment and which maintains the above-referenced device characteristics.